The present disclosure relates to final and provisional implants used in knee arthroplasty, and, in particular, to final and provisional patellar implants for replacing a patellar articular surface and facilitating the proper placement of a patellar implant, respectively.
The knee joint is generally formed by the pair of condyles located at the distal portion of a femur, the tibial plateau located at the proximal end of a tibia and a pair of menisci positioned between the tibial plateau and the femoral condyles. The knee further includes the patella which is secured by the patellar tendon to ride against an anterior portion of the femur during articulation of the knee.
A knee may experience disease or trauma necessitating replacement of all or a portion of the knee with one or more prosthetic knee implants including prosthetic components such as a femoral component to replace the distal end of the femur, a tibial component to replace the proximal end of the tibia, a bearing insert to replace articulating tissue between the femur and the tibia and a patellar articular surface to replace the articulating surface of the patella. During replacement of the patellar articular surface, the patella may be everted to provide access to its posterior surface so that the posterior surface of the patella can be shaped to accommodate placement of a prosthetic patellar component thereon.
Knee prosthesis systems may include different sized femoral components, tibial components, bearing inserts and patellar articular surfaces. Patellar articular surfaces of differing sizes many times utilize differing securement mechanisms so that intraoperatively switching from one size to another necessitates altering the compatible securement features formed in the natural patella which receives the prosthetic patellar articular surface. In certain pre-existing systems, such as the Zimmer Natural Knee II System, a series of differently sized circular patellar prostheses may utilize compatible securement features so that the associated securement features formed in the natural patella do not have to be re-formed when intraoperatively choosing between two different size patellas. The patellas of this system all have a mathematically similar, i.e., circular perimeter shape. The Zimmer Natural Knee II System is shown and described in the Natural-Knee II Primary System Surgical Technique bearing copyright dates of 2004, 2005 and 2009, a copy of which is herewith submitted in an Information Disclosure Statement, the entire disclosure of which is hereby explicitly incorporated by reference herein.